Realistically, it's tough for concave to "die." You're more likely to snap the board before that happens. Stability is 90% rider, 10% gear. With that being said though, you usually want to avoid boards with flex for that to be true. Another thing you can do is switch the bushings out to harder ones from various companies like Riptide, Venom, etc.

With drop through trucks, a lot of people like them because it makes them feel like they're lower to the ground, thus, more stable. I disagree with the stability part because realistically, you want to be standing on, or right behind the bolts for maximum control over the trucks. Also, you are correct in that the hole itself for the trucks theoretically weakens the board. Though, again, the chances of that actually happening are fairly slim.

Wheels wise, at your weight, you can technically get away with a slightly harder wheel, IE: 83a+, though, that is not a set rule of thumb. A common misconception is that the harder the wheel, the easier/better the slide. That is not always true. What you want to look for in a wheel that is more slide orientated are skinny lips, and a skinnier profile.

Like that. For most companies, having a softer duro just means that the wheel will die faster.

Check out Silverfishlongboard.com as well if you want more resources and information on longboarding stuff. The only thing that I do need to warn you about is that there is a good chance you will get flamed into oblivion if you don't take the time to research your question before making a new thread.